Gettering arrangements for vacuum-type circuit interrupters comprising fibers of gettering material embedded in a matrix of material of good conductivity

ABSTRACT

To provide a gettering action in relatively high-power vacuumtype circuit interrupters, an active gettering material, such as titanium, tantalum, columbium, zirconium, tungsten or molybdenum is incorporated in the electrode structures or interior elements of a vacuum-type circuit interrupter, so as to be subjected to the heat of the arc, which is established during circuit interruption. By the raising of the temperature of the gettering materials, or agents, their gas-absorption characteristics are activated. The gettering materials are incorporated as filaments, or rods, either disposed randomly, or in parallel alignment in a matrix of good conducting material, such as copper or silver, in the contact portions, so as to be subjected to the heat of arcing.

United States Patent 2,121,180 6/1938 Vatter Joseph Lempert Pittsburgh,Pa.;

Gerald R. Kotler, Oak Park, Mic 714,197 Mar. 19, 1968 July 13, 1971Westinghouse Electric Corporation Pittsburgh, Pa.

Inventors Ap No. Filed Patented Assignee GET'I'ERING ARRANGEMENTS FORVACUUM- TYPE CIRCUIT INTERRUPTERS COMPRISING FIBERS OF GETTERINGMATERIAL EMBEDDED IN A MATRIX OF MATERIAL OF GOOD References CitedUNITED STATES PATENTS ZOO/144 (.2)

2,794,885 6/1957 Jennings 200/144 (.2)

3,158,719 11/1964 Polinko, Jr. et a1. ZOO/144 (.2)

3,270,172 8/1966 Chubb ZOO/144(1) 3,379,846 4/1968 Wood eta]. 200/144(.2) FOREIGN PATENTS 351,131 6/1931 Great Britain................ZOO/144(2) 403,937 4/1932 Great Britain .2)

Primary Examiner-Robert K. Schaefer Assistant Examiner-Robert A.Vanderhye Attorneys-A. T. Stratton, C. L. McHaIe and W. R. CroutABSTRACT: To provide a gettering action in relatively highpowervacuum-type circuit interrupters, an active gettering material, such astitanium, tantalum, columbium, zirconium, tungsten or molybdenum isincorporated in the electrode structures or interior elements of avacuum-type circuit interrupter, so as to be subjected to the heat ofthe arc, which is established during circuit interruption. By theraising of the temperature of the gettering materials, or agents, theirgas-absorption characteristics are activated. The gettering materialsare incorporated as filaments, or rods, either disposed randomly, or inparallel alignment in a matrix of good conducting material, such ascopper or silver, in the contact portions, so as to be subjected to theheat of arcing.

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PATENTED JUL] 3 I97! SHEET 2 [IF 3 FIG.|3.

FIG.IO.

FIGS.

GETTERING ARRANGEMENTS FOR VACUUM-TYPE CIRCUIT INTERRUPTERS COMPRISINGFIBERS OF GETTERING MATERIAL EMBEDDED IN A MATRIX OF MATERIAL OF GOODCONDUCTIVITY BACKGROUND OF THE INVENTION The present invention relatesto gettering arrangements in vacuum-type circuit interrupters formaintaining the pressure within such an interrupter at the desired lowlevel over a prolonged period. Successful operation of a vacuum-typecircuit interrupter depends to an important extent upon the maintenanceof a very low pressure within the interrupter. If the static pressurewithin the interrupter is allowed to Auerbach exceed a value of aboutTorr for devices of usual dimensions, the dielectric strength of thevacuum becomes impaired, and, as a result, the likelihood of a breakdownbetween the parts of the interrupter greatly increases. In addition, ifany significant amount of gas is present in the interrupter for anappreciable period, it tends to be adsorbed by, or react with thesurfaces of the device, and a high voltage breakdown is more likely tobe initiated from a relatively dirty surface, such as this, than from agas-free surface.

Moreover, an excessive pressure within the interrupter can seriouslyimpair the ability of the interrupter to perform its intendedinterrupting operation. In this regard, the usual vacuum-type circuitinterrupter comprises a pair of separable contacts disposed within anevacuated envelope. Circuit interruption is initiated by separatingthese contacts, thus establishing an arc across the resulting gap.Assuming that the circuit is an altemating-current circuit, the arcmaintains itself until about the time a natural current zero is reached.The are then vanishes, and the usual recovery voltage transient beginsbuilding up across the gap, in some cases approaching a peak value oftwice normal system voltage. If the interruption is to be a successfulone, the vacuum interrupter must have a sufficiently high dielectricstrength during buildup of the recovery voltage transient to prevent thetransient or the subsequent peak AC voltages which are impressed acrossthe interrupter from breaking down any of the electrically stressed gapsof the interrupter. I

Any significant amount of free gas present inside the interrupter, or onthe surfaces of the interrupter during this interval, could interferewith establishment of the required dielectric strength across thestressed gaps of the interrupter, and the recovery voltage transientwould breakdown these gaps. Accordingly, it is highly desirable tominimize the amount of gases present within the interrupter, and tomaintain the pressure at a low level, preferably below l0 Torr.

U.S. Pat. No. 3,090,852 issued to Allan Greewood teaches the concept ofemploying a getter element that is operable, when heated to apredetermined temperature, to clean up gases present within theevacuated envelope of a vacuum-type circuit interrupter. For heating thegetter element to the predetermined temperature during normal operationof the vacuum interrupter, he provides a saturable core of magnetizablematerial disposed about the circuit-interrupter conductor, and asecondary winding inductively coupled to the core. The getter element iselectrically connected across the terminals of the secondary winding.The core has magnetization characteristics that causes saturation of thecore to occur at a level of current through the conductor notsubstantially exceeding the rated continuous current of the interrupter.Also Australian Pat. No. 236,915 issued Apr. 14, 1960 to Kenneth WilliamBrown teaches the concept of utilizing gettering materials within thecontacts of a vacuum-type circuit interrupter. Brown utilizes zirconium,titanium and thorium as his getter materials.

SUMMARY or THE INVENTION According to the present disclosure, a suitablegetter material, such as titanium, tantalum, columbium, zirconium,tungsten, or molybdenum is located in a strategic position within theevacuated envelope of the vacuum circuit interrupter, so as to be heatedby the are, which is established during a circuit-interrupter openingoperation. As a result, some of the getter material is evaporized andsputtered, and provides a layer of the fresh elemental getteringmaterial on certain portions of the interior of the evacuated envelope.In one particular gettering arrangement, a disc of titanium, forexample, is provided rearwardly of one of the separable contacts of avacuum circuit interrupter. In another gettering arrangement, thegettering material is provided as a ring surrounding the contact of theinterrupter. According to the present invention, the gettering materialis provided in filamentary or columnar form and infiltrated with copperor silver to provide a mechanically high-strength contact material.

In still another form of gettering arrangement, the gettering material,in wire form, is compacted and infiltrated with a suitable metal, suchascopper or silver, of relatively high conductivity, so that the getteringmaterial is immediately adjacent the established arc, and is evaporizedand sputtered during the arc-interruption operation.

Accordingly, it is a general object of the present invention to providean improved vacuum-type circuit interrupter in which improved getteringarrangements are provided.

Still a further object of the present invention is the provision of animproved vacuum-type circuit interrupter in which residual .gases areeliminated by interposing gettering materials at strategic locationswithin the vacuum interrupter envelope so as to be heated and sputteredduring a normal circuit-interrupting operation, hence deposited on theinterior walls of the interrupter to provide high speed gettering.

Still a further object of the present invention is to incorporategettering materials in fiber form, within the contact structure so as tobe subjected to the discharge effects associated with the arc and as aresult deposited on the interior walls of the interrupter.

As well known by those skilled in the art, contact members forelectrical circuit making and breaking devices should have lowelectrical resistance, low contact drop, resistance to sticking, wearresistance and low chopping current. Good conducting metals such, forexample, as copper and silver which have relatively low melting pointshave poor wear resistance, and are not entirely satisfactory as contactmembers for continuous usage. Refractory metals such as tungsten,molybdenum, or tantalum, which have satisfactory resistance to wear andsticking, are generally poor conductors having a high contact drop andhigh electrical resistance. Contacts of these refractory metals becauseof their lower electrical and thermal conductance and lower vaporpressure are limited in the current they will interrupt by theirtendency to reach very high temperatures where large and uncontrollablethermonic currents can be emitted. Higher vapor pressure materialsoperate at lower electrode temperatures because of vapor cooling asevaporation takes place.

It is a distinct purpose of the present invention to provide contactmembers for vacuum-type circuit interrupters in which the contactmembers will have a low resistance, low contact drop, resistance tosticking and wear, low chopping currents and yet will provide adjacentthe arcing region gettering materials which will have a very rapidcontinuous pumping action to remove residual gases from the interior ofthe vacuum envelope, or gases which are released from the electrodes asa result of the erosion to the electrodes which occurs on interruptionwhich, as mentioned may lead to dielectric breakdown.

Further objects of the invention will readily become apparent uponreading the following description taken in conjunction with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view ofa vacuum-type circuit interrupter embodying one form of our device;

FIG. 2 is a considerably enlarged fragmentary view of one of thecontacts utilized in the circuit interrupter of FIG. 3 is an alternateform of gettering arrangement associated with one of the contacts of thevacuum-type circuit interrupter, the view being taken partially insection along the line lIl-III of FIG. 4;

FIG. 4 is a top plan view of the contact structure illustrated in FIG.3;

FIG. 5 illustrates a plurality of short fibers or wires of getteringmetal;

FIG. 6 illustrates the fibers illustrated in FIG. 5 after they have beencompressed into the form of a contact member;

FIG. 7 is a vertical sectional view taken through an induction heatingfurnace for infiltrating the gettering wire of FIG. 6 with aninfiltrating good conducting material, such as copper or silver, in anevacuated environment or in a hydrogen environment;

FIG. 8 illustrates a modified type contact structure;

FIG. 9 illustrates a contact member made by infiltrating the compressedform of contact of FIG. 6 with a good conducting metal in the apparatusof FIG. 7;

FIG. 10 is an elevational view of a composite contact bar that has beenformed in accordance with the principles of this invention, and cut intoa plurality of contact members;

FIG. 11 is an enlarged view of a section of the contact surface of oneof the contact members shown in FIG. 10;

FIGS. 12 and 13 illustrate different embodiments of the invention shownin FIG. 10;

FIG. 14 is a vertical sectional view taken through a modified-type ofseparable contact structure in which an arcinitiating region and anarc-running region is utilized, and the arc-running region is providedby a composite contact structure of the type illustrated in FIGS. 913 ofthe drawings;

FIG. 15 is a perspective view of the general type of contact structureillustrated in FIG. 14, wherein the arc is caused by magnetic action torotate circumferentially about the arcrunning region,- which is made ofthe composite contact material incorporating a gettering element; and,

FIG. 16 illustrates contacts made by a sintering mixture of powder metalwith a good conducting metal, heating taken place in a furnace of thetype illustrated in FIG. 7 of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS When the electrodes of a vacuumswitch are opened at the beginning of a given interruption, a metallicarc initiates between the separating electrodes, and serves as a vehiclefor current conduction until the normal alternating current cyclicvariation of current drops the magnitude of the current below thechopping current. At this value of current, the mechanisms which causethe arc to extinguish predominate over those, which sustain the arc, andit goes out. Because of the high-power density impressed on theelectrodes during the conduction interval, substantial erosion takesplace releasing gas adsorbed on the surface and contained within thevolume of the electrode proper.

The substantial erosion of the interrupter electrodes is not confined tothe interruption operation but also occurs when the contacts are closedunder load to permit nonnal operation of the associated circuitry. Theopen position, which may be as much as one-half inch, has the dielectricstrength to withstand the open circuit voltage. As the electrodes areclosed, however, the gap length decreases to a value where arc-overoccurs. The arc persists until the interrupter reaches the fully closedposition, causing further erosion of the electrodes.

One of the principal problems associated with the manufacture ofvacuum-tube interrupters concerns the quantity of gas evolved during aninterruption. If the release of gas from the electrodes producespressures in the micron range, when the interrupter is in the openposition, a discharge will be initiated as soon as the dielectricstrength of the vacuum dielectric is exceeded during the alternatingcurrent wave, and a restrike occurs, or indeed, no interruption takesplace at all. Consequently, it is necessary to subject the components ofthe tube during interruption manufacture to very stringent outgassingprocedures which are time consuming and expensive to insure an absenceof restrikes and to produce the desired interruption reliability. Thepenalties for inadequate outgassing of the tube are severe. In the firstplace, failure of the tube to extinguish will cause premature tubefailure due to the high loadings, which will melt and damage componentsof the tube. Secondly, it may also result in injury to the electricalequipment being protected by the vacuum switch.

Referring now to the vacuum interrupter of FIG. 1, there is shown ahighly evacuated envelope 1 comprising a casing 2 of suitable insulatingmaterial, and a pair of metallic end caps 3 and 4 closing off the endsof the casing. Suitable seals 5 are provided between the end caps andthe casing to render the envelope vacuum-tight. The normal pressurewithin the envelope 1 under static conditions is lower than 10 Torr. sothat a reasonable assurance is had that the mean free path for electronswill be longer than the potential breakdown paths in the envelope.

Located within the envelope 2 is a pair of relatively movabledisc-shaped contacts or electrodes 7 and 8 shown in full lines in theirseparated, or open-circuit position. When the contacts are separated,there is an arcing gap 9 located therebetween. The upper contact 7 is astationary contact suitably secured to a conductive rod 10, which at itsupper end is united to the upper end cap 3. The lower contact 8 is amovable contact joined to a conductive operating rod 11, which issuitably mounted for movement. The operating rod 11 projects through anopening 12 in the lower end cap 4, and a flexible metallic bellows 13provides a seal about the rod 11 to allow for movement of the rodwithout impairing the vacuum inside the envelope 2. As shown in FIG. 1,the bellows 13 is secured in sealing relationship at its respectiveopposite 'ends to the operating rod 11 and to the end cap 4.

Coupled to the lower end of the operating rod 11, suitable actuatingmeans (not shown) is provided for driving the movable contact 8 upwardlyinto engagement with the stationary contact 7 so as to close theinterrupter. The closed position of the movable contact is indicated bythe dotted line 14. The actuating means is also capable of returning thecontact 8 to its illustrated solid-line open position so as to open theinterrupter. A circuit-opening operation will, for example, entail atypical gap length, when the contacts are fully separated, of perhapsone-half inch.

The are (indicated at 15) that is established across the gap 9 betweenthe electrodes, as the electrodes are opened and also when they areclosed, vaporizes some of the contact material, and these vapors aredispersed from the arcing gap 9 toward the envelope 2. In theillustrated interrupter, the internal insulating surfaces of the casing2 are protected from the condensation of arc-generating metallic vaporand particles thereon by means of a tubular metallic shield 16 suitablysupported on the casing 2 and preferably isolated from both end caps 3and 4. This shield 16 acts to intercept and to condense aregeneratedmetallic vapors before they can reach the casing 2. To reduce thechances for vapor bypassing the shield 16, a pair of end shields l7 and18 are provided at opposite ends of the central shield 16.

The vacuum interrupter is an unusual electronic tube, inasmuch as normaloperation of the interrupter, that is the normal service of opening andclosing contacts, causes an unusual amount of electrode erosion. Asmentioned previously the interrupter must be processed duringmanufacture so as to minimize the amount of gaseous contaminantsdissolved in the electrode structure and adsorbed on the internalsurfaces of the interrupter, since as explained previously, pressures ofthe order of a micron, even though of transient duration, can causepermanent failure of the tube and possible injury to associatedcircuitry.

It is well known that the speed of diffusion of gas molecules or atomsfrom a solid is proportional to the concentration of the gaseous specieswithin the solid. For this reason it is very expensive and difficultduring the fabrication of a vacuum interrupter to outgas the electrodesto the desired extent, which is to achieve a freedom of gaseouscontamination of the order of 1 part per million. In conventionalelectronic tubes the outgassing is usually accomplished by heating theelectrodes at a higher temperature than they are expected to encounterin service. Since gaseous diffusion is slower in the operation of theusual electronic tube than it is during exhaust due to the lowertemperature and the low gas concentration gradients present in a welloutgassed tube electrode, no difficulty with gas is usually encounteredin service with conventional electronic tubes.

The contrary situation holds in a vacuum interrupter. The surface of theelectrodes which melt in service necessarily reach higher temperaturesthan can be imposed during exhaust. The low concentration gradient whichmay be expected in a well outgassed part is of no assistance duringinterrupter operation since the forces which hold the gaseouscontaminant within a solid or liquid no longer apply for that portion ofthe electrode material which is vaporized and deposited on neighboringparts of the tube. For this reason the extremely fast and instantaneousgetter disclosed can be used to lower the cost of the tube manufacturesubstantially for the interrupters having low current ratings, and usingthe shielded getter electrode structures also disclosed can be used toincrease rated current capabilities and to lower fabrication costs fortubes interrupting more than 8000 or 10,000 amperes.

A variety of gases are released during opening and closing of electrodesincluding hydrogen carbon monoxide (CO), and carbon dioxide (C0,). Thesegases are eliminated, according to the present invention, by a gettersuch as titanium or zirconium. As shown in FIG. 1, and in the enlargedview of FIG. 2, there is provided a disc of gettering material on therear side of one or both of the separable contacts 7, 8. The result ofsuch a construction is a vacuum interrupter l which will provide ahigh-speed gettering to increase vacuum-switch reliability. Fastgettering is obtained by providing a fresh surface of sputtered gettermaterial 21 as a result of each individual interruption, when the needfor high-speed gettering is at its maximumQIn the following discussionof the disclosed principles of the invention, titanium will be used asan example of a suitable gettering material 21. Other materials,however, such as tantalum, columbium, zirconium, are particularlyappropriate for use in this application. Tungsten and molybdenum mayalso be used.

FIG. 2 shows the general design of an electrode structure usedsuccessfully in a vacuum circuit interrupter. This electrode structuresuccessfully interrupted over 1,200,000 integrated amperes in lifetesting. Pressures were substantially lower than those experienced withthe same electrodes without the provision for high-speed titaniumgettering element 2].

The general objective of the construction illustrated in FIG. 2 is tolocate the titanium disc 20 in a region of the vacuum interrupter whereit will participate in the discharge action 15. The sputtering oftitanium, resulting from the exposure of titanium to the generaldischarge associated with a given interruption or electrode closing,will produce freshly deposited titanium 21 on the internal shield 16 andother surfaces of the vacuum interrupter, thus making available a largearea clean fresh titanium surface, which has a very high gettering speedas a result of its large area and its initial cleanliness and freedomfrom adsorbed gases. High-speed gettering action not only takes place onthe internal surfaces of the interrupter but also during the transit ofthe titanium ions and atoms to the walls of the vacuum interrupter.

The mechanism of gettering of the sputter ion deposited titanium film iscomplex and depends on the type of gas being gettered. The hot freshdeposited titanium surface reacts instantaneously with the ambient gasfonning stable chemical compounds, such as titanium oxides and nitrideswith oxygen and nitrogen gases respectively. 'Ion burial plays animportant role in pumping hydrogen and noble gases, while othermechanisms allow removal of complex molecules, such as the hydrocarbons.

An extremely important feature of the disclosed means of gettering isthat a fresh clean uncontaminated gettering surface 21 is provided witheach closing or opening operation. In conventional electronic tubesgettering is obtained by deposition of a film of getter material such asbarium on an interior wall of the tube. The customary service of agetter layer tends to slow down the gettering action with time since themore exposed portions of the surface quickly get saturated with gas asthe gettering action proceeds. Further gettering takes place as a resultdiffusion of the gaseous contaminant to the interior of the getterlayer, an inherently slow process. Ti and Zr films also have similarcharacteristics which quickly slow down the speed of gettering as thegettering proceeds.

In certain electron tubes filaments of zirconium are heated totemperatures of the order of 850 C. for use as getters. It is stillnecessary for a diffusion process to occur to permit the gaseouscontaminant to combine with getter material in the interior of the wire,after the surface layer has reacted with gas. Furthermore such getterwire structures are usually small in area to minimize power dissipationand thus have relatively slow gettering speeds.

Thus in an application where fast gettering is imperative if it is to beuseful, the disclosed automatic mechanism for providing fresh unexposedfilms of the gettering material as required over a large internal areaof the interrupter, and as a result accomplishing a very high speed ofgettering, is extremely advantageous. The fact that additionalmechanisms for gettering are available as a result of the combination ofthe gaseous contaminant with ions and atoms in transit from the getterreservoir to the interior walls of the interrupter is an important plusfeature, which makes the disclosed structure an even more significantadvance over the state of the art.

Regardless of the specific mechanisms involved, it is an experimentalfact that the gettering action resulting from participation by thetitanium surfaces 22 in the discharge 15 associated with theinterruption, produces a drastic reduction in the pressures that arebuilt up within the vacuum switch 1 as the result of circuitinterruptions and are extinctions.

According to the present disclosure, it is intended to include locatingthe titanium and/or other gettering metal 20 selected in an area of thevacuum interrupter, which is exposed to the sputtering discharge action15. Suitable areas include the condensing shield 16 and the end shields17, 18, as well as the electrodes 7, 8. Specifically excepted would beareas of the vacuum interrupter, which would throw the active getteringmetal onto the glass 2, since this would affect the dielectric strengthof the envelope 2, and lead to premature breakdowns. Also specificallyexcepted is the portion of the electrode structure which makes contactwhen the electrodes are in the closed position. The excepted sections ofthe electrode structure include surface .t" of FIG. 2, surface 8' ofFIG. 3 and 19 of FIG. 14. We prefer to use copper and copper alloys,such as copper bismuth, as the material for the direct contact to thearc 15 to avoid electrode sticking problems in the contact region, andto provide low chopping currents. The main objective in the placement ofthe gettering material 20 is to maintain a reservoir, or supply ofgettering material 21 to supply fresh material as required.

The rate of erosion of the electrodes 7 and 8 exposed to the full'arcl5, and hence the rate of gas evolution from them is a function of theinterruption current. A very advantageous feature of the disclosedmethod is that the amount of titanium 21 sputtered from the surfaces 22is also proportional to the current being interrupted. Thus, thedisclosed principle has a selfcompensating feature, which increases thegettering capability in proportion to the gettering requirement.

FIGS. 3 and 4 illustrate a modified type of electrode construction 24 inwhich a ring of titanium or zirconium 25 is brazed on the rear side ofthe butt-type contact 8'. Tests on this construction consisted of aseries of direct-current interruptions at 200 amperes in a demountabletube. During the first run, the test electrodes were outgassed byconnecting the switch to an exhaust system, and in subsequent runs, thesystem was sealed off from the pumps, and observations made as to therate of rise of pressure as a function of the number of interruptions.In the vast majority of tests on electrode structures and materialswhich did not utilize getter materials, a significant pressure rise wasnoted as a function of the number of interruptions applied once theswitch 1 was sealed off. The demountable tube was, in fact, used toassess the relative quantity of gas held in different electrodematerials. In the case of both tests with titanium 21 participating inthe discharge, a significant drop in pressure was noted as a function ofthe number of interruptions for the tests with the switch sealed off,contrary to experience when no getter materials were employed as part ofthe electrode structure.

Since titanium alloys mix rapidly with copper, it is necessary infabricating the electrode assembly 24 not to expose the copper-titaniumjoint 26 to excessive temperatures. A lowmelting eutectic forms at 900C. In fact, in fabricating the tube, the titanium disc 25 was joined tothe copper 8' without solder by the simple expedient of heating thetitanium-copper assembly 24 to 900 C. in vacuum, and allowing theeutectic, which forms at the interface, to effect the braze. Both ofthese two components of the electrode assembly 24 were outgassed at hightemperature at pressures in the to 10 Torr range prior to the eutecticjoining procedure described above. It is, however, important to designthe interrupter tube so that temperature gradients cannot build upduring the operation of the tube within its interruption ratings whichwell exceed the eutectic temperature. The high temperature solubilityproblem associated with the use of the copper-titanium structures doesnot exist with structures utilizing copper and tantalum, molybdenum ortungsten, since these refractory materials have an extremely lowsolubility for copper, and' vice versa. Thus copper casting techniquescan be utilized when Ta, W or Mo mixtures with Cu are used as the getterreservoir material. Low alloying action between Cu, and Ta, W and Mohelps in keeping the conductivity of the copper high.

Nothing which has been said before should be interpreted as indicatingthat the gettering reservoir 21 needs to be a pure material. In someinstances, it is desirable to use a composite metal structure consistingof two or more metals from the standpoint of increasing the heatdissipation efficiency of the electrode system. For example, a techniquefor taking advantage of the high thermal conductivity associated withcopper, is to use molybdenum, tantalum or tungsten in either fine wireor powder form within a cast or sintered copper matrix as describedhereinafter.

One advantage of the use of tantalum as the gettering material 21 is thefact that it is easier to outgas than copper. The recommended procedurefor fabricating an electrode, consisting of tantalum, tungsten ormolybdenum impregnated in copper is the following: Assume a 60 percentweight percent of the refractory metal. Using 2 to 5 mil tantalum wire,compress a conglomerate or ball of the wire into a small button 23, say,for example, 1 inch long and 1% inches in diameter, in a suitablefixture (not shown). Place the compressed fine wire button 23 in adegassed graphite crucible 28, as shown in FIG. 7, about 1 inches indiameter. Place the desired amount of copper 29 above the button 23 inthe crucible 28. Bring the copper 29 to melt in vacuum using suitabletechniques, such as radiofrequency heating. When the copper melts, itwill impregnate the wire button 23 fully. Upon solidification, thedesired composite electrode assembly 46 (FIG. 9) is obtained. Byadjusting the percentage of getter material 21, and the location of thismaterial within the tube 2, it is possible to arrange for the desiredrelease of gettering material 21 as a function of the required rate ofloading of the interrupter. The percentage of getter material 21 in aconducting matrix like copper, silver or gold can vary from 5 percent to97 percent.

In addition to locating the gettering surfaces 22 in the mannerindicated above, it can also be used as fabricated in thetantalum-copper mix 46, described above, to replace the outer spiralstructure 32 illustrated in FIGS. 14 and 15. As set forth in U.S. Pat.No. 3,182,156, issued May 4, 1965 to Lee et 8.... al., thearc-initiating portion or annulus 19 may be formed of a low-choppinglevel metal or alloy, such as an alloy of Cu with tin, antimony, lead,zinc, bismuth and other metals. However the outer arc-running surface32, of FIG. 14 may be adapted for high-current interruption, andaccording to the present invention can be fabricated using for example atantalum copper getter electrode fabricated as described herein. Theadvantage of the use of such an electrode assembly is that the releaseof getter during operation of the interrupter permits substantiallylower manufacturing costs as a result of the shorter less stringentexhaust schedules which can be employed in manufacturing theinterrupter.

For interrupters having ratings in excess of 8000 or 10,000 amperes weprefer to use the structures shown in FlGS. 2 and 8 in which the getterreservoir is in a partially protected position. The spacing between theouter arc-running electrode 8 and the gettering reservoir 20 of FIG. 2and the diameter and the thickness of getter reservoir 20 can beadjusted in the design of the interrupter electrode to release an amountof getter appropriate to the current being interrupted, and the quantityof gas which will be released in a given interruption.

It is a further purpose of the invention to embed refractory metalshaving good wear resistance and good resistance to sticking within amain base member of a good electrical conducting metal. lt is a purposeof the invention to locate the refractory metal 21 within the contactmember 7, 8 so as not to interrupt the continuity of the electrical paththrough the good conducting metal.

The refractory gettering metals, which have been found to provideexcellent wear resistance and resistance to sticking, are the getteringmetals tantalum, tungsten and molybdenum, particularly in wire or rodform. The members are preferably of an elongated shape with any generalcross section. A further characteristic which will be desirable in therefractory gettering members is the property of being wetted by moltengood conducting metal and with a good bond being formed onsolidification.

The main body of the contact members is composed of a good conductingmetal such, for example, as copper and silver. The properties which aredesirable for the main electrode body metals are good electricalconductivity. Copper and silver base alloys, while they may not have asgood conducting characteristics as pure silver or copper, may besuitable for application in contact members, and it is contemplated tomake use of them in this invention.

The copper and silver will not form a good alloy with tantalum, tungstenand molybdenum gettering materials, since these metals do not form solidsolutions. Thus, it is not possible to alloy the good conducting metalwith a refractory metal to secure a combination of their desirableproperties. It is accordingly, necessary to mechanically intermingleselected shapes of each of these groups of metals and by proper castingor other uniting treatment, form a unitary contact member body.

In order to secure the combined advantages of the good conductingmetals, copper or silver, and the refractory metals, tungsten ormolybdenum, it is proposed to make electrical contact members embodyingelements of the refractory gettering metal in a parallel relationrelative to the direction of currentflow and extending substantiallyentirely through a cast bonding base member composed of good conductingmetal. In this way the continuity of the electrical path through thegood conducting metal is not interrupted by the refractory getteringmetal.

As set forth in U.S. Pat. merchandising 2,295,338, issued Sept. 8, 1942to James K. Ely, and assigned to the assignee of the instantapplication, such a construction may be obtained by molding a pluralityof refractory gettering rods of tantalum, tungsten, molybdenum, or otheractive gettering metals within a mold in which the base metal of copperor silver, or their alloys, is poured in molten form. In the exampleswhich follow, the combination of Ag and W are used as examples. Apreferred combination of materials is Cu and Ta. In addition whilecasting in hydrogen (H furnaces is used as an example of a possibletechnique, we prefer to fabricate electrodes in a vacuum furnace atpressures less than l Torr to avoid H contamination and the necessity ofspecial outgassing procedures to eliminate the H which would be pickedup in an H furnace operation.

Still another method for fabricating the improved contact structures ofthe present disclosure in which a gettering agent 21 is disposed in thevicinity of the contact surface to provide a continuous gettering actionduring arc interruption, is set forth in U.S. Pat; No. 3,254,189, issuedMay 31, 1966 to .I. Evanicsko, Jr. and Charles Deibet, and likewiseassigned to the assignee of the instant application.

The present invention is concerned with an improvement in the method offabrication of contacts in that the contact members 34 may have aconsiderably higher percentage of surface area and volume of thegettering metal 21. In more detail, with reference to FIGS. -13, anelongated composite mass or bar 35 made in accordance with principles ofthis invention, and comprising a plurality of elongated fibers or wires36 of refractory gettering metal selected from the group of tantalum,tungsten, molybdenum and their alloys. The refractory fibers 36 areembedded in a matrix of good conducting metal 37 selected from the groupof copper, silver and their alloys. The elongated composite bar 35 iscut into five sections, as seen in FIG. 10. Each of the three innersections 34 has two contact surfaces 38 at its opposite ends. The outersections 34 have finished contact surfaces 38 at their inner ends; butthe refractory wires 36 must be machined off of the outer ends 39 beforethese contact members 34 are ready for use.

The elongated composite mass or bar 35 shown in FIG. 10 is formed bybunching together the elongated tantalum or tungsten refractory fibersor wires 36 and infiltrating the bunched fibers with the good conductingmetal 37. The elongated refractory fibers 36 are bunched together in agenerally parallel relationship. It is to be noted, however, that theserefractory fibers 36 are randomly distributed in the bunch.

One method of fonning the contact members 34 is to bunch the elongatedrefractory fibers 36 in a generally parallel relationship; the spacingbetween the fibers being determined merely by contact of the fibers 36with each other. The elongated bunched fibers 36 are then held togetherat various points along the elongated bunch by means of wire or fiberwrappings (not shown), or by any other suitable means. The bunchedfibers 36 are then infiltrated by continuously running the bunch througha bath of molten infiltrant of good conducting metal 37 selected fromthe group of copper, silver and their alloys. The infiltrant 37 isallowed to cool and solidify, whereupon the composite bar 35 can be cut,as shown in FIG. 10, into individual contact members 34 by means of anabrasive wheel, or any other suitable tool. The refractory fibers 36that protrude from the outer ends of the outer contact members 39 arethen cut off with an abrasive tool, so that each of these outer contactmembers 39 will have a contact surface 38 at each end thereof.

FIG. 11 represents a view of one of the contact surfaces 38 of thecontact members 34 of FIG. 10. In the particular contact surface shownin FIG. 11, refractory fibers 36 having a 0.005 inch diameter were usedin fonning the contact mem bers 34. Although, as seen in FIG. 11, all ofthe tungsten fibers 36 do not necessarily engage another tungsten fiberat the contact surface, substantially all of these fibers 36 at somepart during the length thereof in the original bundle from which thecontact member was formed, engaged other fibers 36 so that thedistribution of the wires 36 was determined merely by engagement of thefibers with each other. The weight ratio of silver to tungsten in thecontact shown in FIG. 11 is about 25 percent silver to 75 percenttungsten. This ratio can be varied to other desirable percentages byvarying the compactness of the tungsten fiber bundle, and/or by varyingthe diameter size of the tungsten fibers 36 used in the bundle.

Another method of making the contacts 34 shown in FIG. 10 is to place anamount of powdered or solid good conducting metal, selected from thegroup of copper, silver and their alloys, into a mold or container (notshown). A plurality of elongated refractory fibers 36, selected from thegroup of tungsten, molybdenum and their alloys, are then bunchedtogether in a generally parallel relationship. The bunched wires 36 areplaced into the container over the powder or solid good conductingmetal. About 1 percent of powdered nickel may also be included with thegood conducting metal. The assembly is then charged into a furnace at atemperature at which the good conducting metal is molten, for hydrogenapproximately ll00 C. with a dry hydrogen atmosphere. The goodconducting metal, aided by the wetting property of the nickel, isdistributed by capillary action throughout the interstices between therefractory fibers 36. The assembly is then removed from the furnace andallowed to cool and harden. The hardened elongated composite mass or bar35 is then removed from the mold or container, and sliced as seen inFIG. 10 to produce the individual contact members 34. As was previouslydescribed the refractory fibers 36 at the outer surfaces of the-outercontact members 39 are machined off of the outer contact surfaces tocomplete the manufacture of these outer contact members 39.

Another method of manufacturing the contact members 34 shown in FIG. 10is to bunch the elongated refractory wires 36, selected from the groupof tungsten, molybdenum and their alloys, together in a generallyparallel but randomly distributed relationship, and insert this bunchinto a mold or container. A good conducting metal 37 selected from thegroup of copper, silver and their alloys is then preheated to a moltencondition, and poured into the mold or container to flow into the moldand fill the interstices between the tungsten wires 36. The assembly isthen allowed to cool after which the hardened composite mass or bar 35is taken from the mold or container and sliced as shown in FIG. 10.

FIGS. 12 and 13 illustrate different embodiments of the invention shownin FIG. 10. The parts in FIGS. 12 and I3 that correspond to like partsof FIG. I have the same reference characters as the like parts in FIG.10 except that the like reference characters of FIG. 12 are primed andthe like reference characters of FIG. 13 are double primed.

The contact members 34 as shown in FIG. 12 are formed by means of thesame methods hereinbefore described with reference to the contactmembers 34 shown in FIG. 10, except that the bunched together elongatedrefractory metal fibers 36' are wrapped and secured together, prior tothe infiltration with the conducting metal, with an elongated wire orfiber 40 selected from the group of tantalum, tungsten, molybdenum andtheir alloys. The wrapping fiber 40 forms a collar around the bundle ofrefractory wires 36 that gives additional strength to the contactmembers 34 and also serves as the securing means to secure thefibers'36' of the elongated bundle together during the manufacturingoperation.

The contact members 34" shown in FIG. 13 are formed by means of the samemethods hereinbefore described with reference to the contact members 34shown in FIG. 10 except that, as can be seen in FIG. 13, the bundle ofrefractory fibers 36" comprises a plurality of refractory fibers thatare braided or stranded into a cable prior to being infiltrated with thegood conducting metal 37". The embodiment shown in FIG. 13 hasparticular significance in the method of manufacture wherein the bundleof refractory fiber is passed through the molten good conducting metal37" during which operating the metal infiltrates into the bundle in thesame manner previously described. During this operation the braid of thefibers 36" serves to hold the fibers together so that additionalsecuring means are not needed.

Another embodiment of the device is shown in FIGS. 5, 6 and 9. FIG. 5illustrates a pile 42 comprising a plurality of short lengths ofrefractory fibers or wires 43 selected from the group of tungsten,molybdenum and their alloys. These short fibers 43 are placed into aclosed-type die, such as the type used in metal powder compaction, andpressure is applied to compact the short refractory fibers into thedesired shape and density. FIG. 6 illustrates a compacted mass 44 formedfrom the short refractory fibers 43 shown in FIG. 5. The compacted mass44 of refractory fibers (FIG. 6), after being removed from the die, isinserted into a container for infiltration. Prior to insertion of thecompacted refractory mass 44 into the container, an infiltrant of goodconducting metal 37 selected from the group of copper, silver and theiralloys is deposited in the container in the form of a powder or a solidpiece. The container is then charged into a furnace at a temperatureabove the melting point of the good conducting metal 37 and below themelting point of the refractory metal. At this temperature the goodconducting metal 37 melts and is distributed by capillary actionthroughout the interstices between the refractory fibers 43. It may bedesirable to put a small percentage of powdered nickel into thecontainer with the good conducting metal so that the wetting property ofthe nickel will aid the capillary action. The mold is then removed fromthe furnace and allowed to cool whereupon the composition 44 solidifies.The composition is then ejected from the mold in the form of a contactmember 46, as shown in FIG. 9.

Although the preferable method of forming the contact member 46 shown inFIG. 9 is to have the good conducting metal 37 in the container underthe compacted mass 44 of refractory metal, it will be understood thatthe good conducting metal can be placed on top of the compacted mass 44,before the assembly is charged into the furnace so that the goodconducting metal, when melted, will flow down through the compacted mass44 to infiltrate into the openings within the mass 44.

The contact member 46 (FIG. 9) can be made in another manner by merelyplacing the compacted mass 44 (FIG. 6)

into a container and pouring molten good conducting metal selected fromthe aforementioned group into the container whereupon the goodconducting metal will fiow down through the compacted mass 44 toinfiltrate within the mass 44.

Another method of forming a contact member, such as the contact member46, shown in FIG. 9, is to merely place the loose short fibers 43, shownin FIG. 5, into a container on top of a powdered or a solid piece ofgood conducting metal 37 selected from the group of copper, silver andtheir alloys, and charge the container into a furnace whereupon the goodconducting metal melts and is infiltrated throughout the openingsbetween the refractory fibers 43 forming a composition that is allowedto cool and solidify and is then ejected from the container as afinishedcontact member 46.

It is to be understood that the container used in molding the contactmembers shown in FIG. 9 can be of considerable depth to produce acomposition, that is similar to that shown in FIG. 9, but which is muchlonger. The elongated composition can be sliced by means of an abrasivewheel, or other suitable tool into contact members 46 having the desireddepth.

The short members 43 (FIG. of refractory metal that are used inmanufacturing the finished contact members 46 (FIG. 9) can be ends ofwires or chips, that might otherwise have been considered scrap. Thus,an advantage of this method of the compacted mass 44 (FIG. 6) isinfiltrated. The refractory fibers, that are disposed throughout thefinished contact member and at the contact surface in a randomorientation, are effective in preventing thermal cracking of the contactunder operation conditions.

The following are examples of contacts made in accordance withprinciples of this invention.

EXAMPLEI Pure tungsten fiber of wire, cleaned and straightened wasobtained in 0.010 inch size. The fiber was wound on a two spindle spoolto form an oblong coil about 4 inches long. Both coil ends were cut andthe two halves were brought together to form a fiber bunch approximatelyfive-eighths of an inch in diameter which bunch was then tightly wrappedwith tungsten fiber. This bundle of fiber was positioned vertically in aceramic crucible containing silver powder plus about 1 percent, byweight, of nickel. The assembly was charged into a furnace 41approximately I l00 C. with a dry hydrogen atmosphere. At thistemperature the molten silver, aided by the wetting property of thenickel, was distributed by capillary action throughout the intersticesbetween the tungsten fiber 36. The assembly was then taken from thefurnace and allowed to cool after which the composition was removed fromthe crucible 28. Separate contact elements or members were then obtainedmanufacture is that material that might otherwise have been wasted canbe utilized in forming improved contact members 46.

A modification of the device shown in FIGS. 5, 6 and 9 comprises theintroduction of a portion of the refractory metal in powder form alongwith the refractory metal fibers. Up to 80 percent of the weight ofrefractory metal selected from the group of tantalum, tungsten,molybdenum and base alloys thereof may be comprised of powderedrefractory metal of approximately l00 mesh fineness, the balance beingfibers of refractory metal, all being more or less homogeneously admixedand then compacted in the same manner hereinbefore described into a slugor mass similar to the slug 44 seen in FIG. 6, except that the slugcomprises the compacted fibers and powder. The compacted slug or mass 44is then infiltrated with a molten good conducting metal selected fromthe group of copper, silver and base alloys thereofin the same manner asfrom this elongated composition by slicing the composition in the mannershown in FIGS. l0, l2 and 13. One of these contact elements was thenmachined to a fz-inch diameter and a .4-inch height. The composition ofthis contact element-as to silver-to-tungsten ratio was determined byarea measurements on a metallographically polished cross section.Because of the fixed diameter of the refractory tungsten wire, the areapercentage is also the volume percentage and this area percentage wasdetermined simply by counting the wires within a fixed diameter circle.The results indicated that this particular contact element had atungsten volume percentage of 62 percent, the remaining 38 percent beingthe silver infiltrant. These figures convert to a weight percentageratio of 25 percent silver- 75 percent tungsten.

EXAMPLE ll Another contact element or member was made in the same mannerin which the contact element discussed in Example I was made except thatthe tungsten fibers 36 were of a 0.005 inch diameter. The resultantcontact element was found to have a 20 percent silverpercent tungstenweight percentage ratio.

EXAMPLE "I Tungsten fiber 36 having a 0.010 inch diameter was cut upinto short lengths similar to that shown in FIG. 5. These short lengthsof fiber were poured into a cavity that has been machined in a block ofgraphite which cavity was 1 inch deep and had a %-inch diameter.Powdered silver was placed on top of the short tungsten fibers, and theassembly was charged into a hydrogen atmosphere furnace for one hour at1 C. This allowed the silver to melt and completely infiltrate thetungsten fibers. The assembly was then removed from the furnace, andallowed to cool. The contact element was removed from the cavity andmachined to a thickness of one-fourth of an inch and a diameter ofone-half inch. The composition of this contact member was determined bymeasuring its density of water displacement, and converting this figureto composition, with the assumption that the member was 100 percentdense. The result showed that the contact element had a weight ratio of80 percent silver-20 percent tungsten.

EXAMPLE IV Tungsten fiber 36 having a 0.005 inch diameter was cut intoshort lengths similar to that shown in FIG. 5. These short lengths werecharged into a closed-type die having a z-inch diameter die cavity andcompacted with a load of tons. The compacted mass was then removed fromthe die and it was found that this mass had a height of about one-halfof an inch and the tungsten fibers occupied about 65 percent of thevolume of the mass. The short tungsten wires interlocked very nicely,resulting in a strong compact mass which retained its shape. Thecompacted mass was then infiltrated with silver by placing it on top ofa 4.0 gram silver disc within a cavity in a graphite block. The assemblywas charged into a hydrogen atmosphere furnace for 30 minutes at l150 C.The assembly was then removed and allowed to cool. The hardened contactmember was removed and machined to the desired size for test purposes.The composition of this contact member was determined by measuring thedensity of the member of water displacement, and converting this figureto composition, within the assumption that the contact member was 100percent dense. Results showed that the contact member to have a weightratio of percent silver-75 percent tungsten.

FIG. 16 illustrates using particles ofa gettering material 21interspersed with particles of good conducting material 37, and heatedin a furnace to melt the lower-melting good conducting material 37. Theresulting contact is hence fabricated by powder metallurgicaltechniques.

From the foregoing description it will be apparent that there has beenprovided improved gettering arrangements for vacuum type circuitinterrupters involving improved electrode assemblies, and contactstructures in which the gettering material is disposed in the vicinityof the arcing region to receive the heat therefrom and thus to cause thevaporization and spattering of gettering material upon interior parts ofthe evacuated envelope of the vacuum-type circuit interrupter.

Although there has been illustrated and described specific structures,it is to be clearly understood that the same were merely for the purposeof illustration, and that changes and modifications may readily be madetherein by those skilled in the art, without departing from the spiritand scope of the inventlon.

We claim as our invention:

1. An alternating-current circuit interrupter of the vacuum typecomprising, in combination:

a. an evacuated envelope;

b. a pair of separable contacts disposed within the evacuated envelope;

c. gettering means disposed within the evacuated envelope disposed innear proximity to the region of arcing between said separable contacts,whereby the effect of the arc is to cause vaporization and sputtering ofthe getter material; and,

d. the gettering means being incorporated in one of the contacts as aplurality of metallic fibers embedded in a matrix of metal of goodconductivity.

2. The combination of claim 3, wherein the fibers have a randomdistribution at the contact surface.

3. The combination of claim 1, wherein the fibers are disposed ingenerally parallel relationship.

4. The combination of claim 3, wherein the fibers are selected from thegroup consisting of titanium, tantalum, columbium, zirconium, tungstenand molybdenum, and the matrix of metal is selected from the groupconsisting of copper, silver and base alloys thereof.

1. An alternating-current circuit interrupter of the vacuum typecomprising, in combination: a. an evacuated envelope; b. a pair ofseparable contacts disposed within the evacuated envelope; c. getteringmeans disposed within the evacuated envelope disposed in near proximityto the region of arcing between said separable contacts, whereby theeffect of the arc is to cause vaporization and sputtering of the gettermaterial; and, d. the gettering means being incorporated in one of thecontacts as a plurality of metallic fibers embedded in a matrix of metalof good conductivity.
 2. The combination of claim 3, wherein the fibershave a random distribution at the contact surface.
 3. The combination ofclaim 1, wherein the fibers are disposed in generally parallelrelationship.
 4. The combination of claim 3, wherein the fibers areselected from the group consisting of titanium, tantalum, columbium,zirconium, tungsten and molybdenum, and the matrix of metal is selectedfrom the group consisting of copper, silver and base alloys thereof.